Digital radio broadcasting technology delivers digital audio and data services to mobile, portable, and fixed receivers. One type of digital radio broadcasting, referred to as in-band on-channel (IBOC) digital audio broadcasting (DAB), uses terrestrial transmitters in the existing Medium Frequency (MF) and Very High Frequency (VHF) radio bands. HD Radio™ Technology, developed by iBiquity Digital Corporation, is one example of an IBOC implementation for digital radio broadcasting and reception.
IBOC DAB signals can be transmitted in a hybrid format including an analog modulated carrier in combination with a plurality of digitally modulated carriers or in an all-digital format wherein the analog modulated carrier is not used. Using the hybrid mode, broadcasters may continue to transmit analog AM and FM simultaneously with higher-quality and more robust digital signals, allowing themselves and their listeners to convert from analog to digital radio while maintaining their current frequency allocations.
IBOC DAB technology can provide digital quality audio, superior to existing analog broadcasting formats. Because each IBOC DAB signal is transmitted within the spectral mask of an existing AM or FM channel allocation, it requires no new spectral allocations. IBOC DAB promotes economy of spectrum while enabling broadcasters to supply digital quality audio to the present base of listeners.
The National Radio Systems Committee, a standard-setting organization sponsored by the National Association of Broadcasters and the Consumer Electronics Association, adopted an IBOC standard, designated NRSC-5, in September 2005. NRSC-5, the disclosure of which is incorporated herein by reference, sets forth the requirements for broadcasting digital audio and ancillary data over AM and FM broadcast channels. The standard and its reference documents contain detailed explanations of the RF/transmission subsystem and the transport and service multiplex subsystems. iBiquity's HD Radio Technology is an implementation of the NRSC-5 IBOC standard.
Other types of digital radio broadcasting systems include satellite systems such as XM Radio, Sirius and WorldSpace, and terrestrial systems such as Digital Radio Mondiale (DRM), DRM+, Eureka 147 (branded as DAB), DAB Version 2, and FMeXtra. As used herein, the phrase “digital radio broadcasting” encompasses digital audio broadcasting including in-band on-channel broadcasting, as well as other digital terrestrial broadcasting and satellite broadcasting.
Antenna diversity techniques are used to mitigate the effects of distortion and outages due to multipath propagation of the received FM signal. Diversity can also accommodate the directional characteristics of glass-embedded window antennas. A variety of diversity antenna techniques have been developed and deployed for use with automotive FM receivers. Although all FM receivers, including tabletop, home theater, and portable receivers, could benefit from antenna diversity, only automotive receivers presently employ diversity techniques. Furthermore, the diversity algorithms developed for analog FM receivers are generally not appropriate for HD Radio digital reception.
It would be desirable to have a metric for the quality of a received radio signal that can be used to control antenna diversity switching, as well as switching control logic appropriate for the IBOC signals.